use configparser::ini::Ini;
use glob::{glob_with, MatchOptions};
use std::collections::BTreeMap;
use std::path::{Path, PathBuf};
use std::time::SystemTime;

static SIDECAR_FILENAME: &str = ".meta";

/// A struct to store a string of metadata for each file retrieved from
/// sidecar files called `.lang`.
///
/// These sidecar file's lines should have the format
/// ```text
/// <filename>:<metadata>
/// ```
/// where `<filename>` is only a filename (not a path) of a file that resides
/// in the same directory and `<metadata>` is the metadata to be stored.
/// Lines that start with optional whitespace and `#` are ignored, as are lines
/// that do not fit the basic format.
/// Both parts are stripped of any leading and/or trailing whitespace.
pub(crate) struct FileOptions {
    /// Stores the paths of the side files and when they were last read.
    /// By comparing this to the last write time, we can know if the file
    /// has changed.
    databases_read: BTreeMap<PathBuf, SystemTime>,
    /// Stores the metadata for each file
    file_meta: BTreeMap<PathBuf, PresetMeta>,
    /// The default value to return
    default: PresetMeta,
}

/// A struct to store the different alternatives that a line in the sidecar
/// file can have.
#[derive(Clone, Debug)]
pub(crate) enum PresetMeta {
    /// A line that starts with a semicolon in the sidecar file, or an
    /// empty line (to overwrite the default language command line flag).
    /// ```text
    /// index.gmi: ;lang=en-GB
    /// ```
    /// The content is interpreted as MIME parameters and are appended to what
    /// agate guesses as the MIME type if the respective file can be found.
    Parameters(String),
    /// A line that is neither a `Parameters` line nor a `FullHeader` line.
    /// ```text
    /// strange.file: text/plain; lang=ee
    /// ```
    /// Agate will send the complete line as the MIME type of the request if
    /// the respective file can be found (i.e. a `20` status code).
    FullMime(String),
    /// A line that starts with a digit between 1 and 6 inclusive followed by
    /// another digit and a space (U+0020). In the categories defined by the
    /// Gemini specification you can pick a defined or non-defined status code.
    /// ```text
    /// gone.gmi: 52 This file is no longer available.
    /// ```
    /// Agate will send this header line, CR, LF, and nothing else. Agate will
    /// not try to access the requested file.
    FullHeader(u8, String),
}

impl FileOptions {
    pub(crate) fn new(default: PresetMeta) -> Self {
        Self {
            databases_read: BTreeMap::new(),
            file_meta: BTreeMap::new(),
            default,
        }
    }

    /// Checks wether the database for the directory of the specified file is
    /// still up to date and re-reads it if outdated or not yet read.
    fn update(&mut self, file: &Path) {
        let mut db = if super::ARGS.central_config {
            super::ARGS.content_dir.clone()
        } else {
            file.parent().expect("no parent directory").to_path_buf()
        };
        db.push(SIDECAR_FILENAME);

        let should_read = if let Ok(metadata) = db.metadata() {
            if !metadata.is_file() {
                // it exists, but it is a directory
                false
            } else if let (Ok(modified), Some(last_read)) =
                (metadata.modified(), self.databases_read.get(&db))
            {
                // check that it was last modified before the read
                // if the times are the same, we might have read the old file
                &modified >= last_read
            } else {
                // either the filesystem does not support last modified
                // metadata, so we have to read it again every time; or the
                // file exists but was not read before, so we have to read it
                true
            }
        } else {
            // the file probably does not exist
            false
        };

        if should_read {
            self.read_database(&db);
        }
    }

    /// (Re)reads a specified sidecar file.
    /// This function will allways try to read the file, even if it is current.
    fn read_database(&mut self, db: &PathBuf) {
        log::trace!("reading database {:?}", db);

        let mut ini = Ini::new_cs();
        ini.set_default_section("mime");
        ini.set_comment_symbols(&['#']);
        let map = ini
            .load(db.to_str().expect("config path not UTF-8"))
            .and_then(|mut sections| {
                sections
                    .remove("mime")
                    .ok_or_else(|| "no \"mime\" or default section".to_string())
            });
        self.databases_read
            .insert(db.to_path_buf(), SystemTime::now());
        let files = match map {
            Ok(section) => section,
            Err(err) => {
                log::error!("invalid config file {:?}: {}", db, err);
                return;
            }
        };

        for (rel_path, header) in files {
            // treat unassigned keys as if they had an empty value
            let header = header.unwrap_or_default();

            // generate workspace-relative path
            let mut path = db.clone();
            path.pop();
            path.push(rel_path);

            // parse the preset
            let preset = if header.is_empty() || header.starts_with(';') {
                PresetMeta::Parameters(header.to_string())
            } else if matches!(header.chars().next(), Some('1'..='6')) {
                if header.len() < 3
                    || !header.chars().nth(1).unwrap().is_ascii_digit()
                    || !header.chars().nth(2).unwrap().is_whitespace()
                {
                    log::error!("Line for {:?} starts like a full header line, but it is incorrect; ignoring it.", path);
                    return;
                }
                let separator = header.chars().nth(2).unwrap();
                if separator != ' ' {
                    // the Gemini specification says that the third
                    // character has to be a space, so correct any
                    // other whitespace to it (e.g. tabs)
                    log::warn!("Full Header line for {:?} has an invalid character, treating {:?} as a space.", path, separator);
                }
                let status = header
                    .chars()
                    .take(2)
                    .collect::<String>()
                    .parse::<u8>()
                    // unwrap since we alread checked it's a number
                    .unwrap();
                // not taking a slice here because the separator
                // might be a whitespace wider than a byte
                let meta = header.chars().skip(3).collect::<String>();
                PresetMeta::FullHeader(status, meta)
            } else {
                // must be a MIME type, but without status code
                PresetMeta::FullMime(header.to_string())
            };

            let glob_options = MatchOptions {
                case_sensitive: true,
                // so there is a difference between "*" and "**".
                require_literal_separator: true,
                // security measure because entries for .hidden files
                // would result in them being exposed.
                require_literal_leading_dot: !crate::ARGS.serve_secret,
            };

            // process filename as glob
            let paths = if let Some(path) = path.to_str() {
                match glob_with(path, glob_options) {
                    Ok(paths) => paths.collect::<Vec<_>>(),
                    Err(err) => {
                        log::error!("incorrect glob pattern in {:?}: {}", path, err);
                        continue;
                    }
                }
            } else {
                log::error!("path is not UTF-8: {:?}", path);
                continue;
            };

            if paths.is_empty() {
                // probably an entry for a nonexistent file, glob only works for existing files
                self.file_meta.insert(path, preset);
            } else {
                for glob_result in paths {
                    match glob_result {
                        Ok(path) if path.is_dir() => { /* ignore */ }
                        Ok(path) => {
                            self.file_meta.insert(path, preset.clone());
                        }
                        Err(err) => {
                            log::warn!("could not process glob path: {}", err);
                            continue;
                        }
                    };
                }
            }
        }
    }

    /// Get the metadata for the specified file. This might need to (re)load a
    /// single sidecar file.
    /// The file path should consistenly be either absolute or relative to the
    /// working/content directory. If inconsisten file paths are used, this can
    /// lead to loading and storing sidecar files multiple times.
    pub fn get(&mut self, file: &Path) -> PresetMeta {
        self.update(file);

        self.file_meta.get(file).unwrap_or(&self.default).clone()
    }

    /// Returns true if a configuration exists in a configuration file.
    /// Returns false if no or only the default value exists.
    pub fn exists(&mut self, file: &Path) -> bool {
        self.update(file);

        self.file_meta.contains_key(file)
    }
}